In electromagnetically-driven rail guns, two metallic rails in the gun barrel (bore) serve as electrodes that conduct current to a metallic armature wedged tightly between the rails. The armature is placed at the back of the projectile that delivers a payload. A fast, high-current pulse loops through the rails via the armature, generating a magnetic field that couples with the current passing through the armature to produce a force that accelerates the projectile down the barrel at supersonic speeds. Exemplary electromagnetic (EM) rail guns are described in U.S. Pat. No. 7,409,900. Nechitailo et al., issued Aug. 12, 2008; U.S. Pat. No. 7,077,047, J. F. Frasca, issued Jul. 18, 2006; U.S. Patent Application No. 20080053299, R. J. Taylor, publication date Mar. 6, 2008: and U.S. Patent Application No. 20070277668, J. F. Frasca, publication date Dec. 6, 2007: all of which are incorporated herein by reference. In presently-designed guns, it has been found that the both the rail and the armature are badly damaged by a combination of arcing, interfacial heating, frictional rubbing and gouging, leading to arc erosion, plowing wear and melting of either or both armature and rail. Although an armature is used only once, loss of armature material, e.g., Al from the low melting temperature Al armature, leads to contamination of rails with metal deposits and, worse, loss of contact between the remaining armature and rail. If the armature metal does not melt (e.g., Cu), arcing at the onset of sliding damages the rail by adding splats of eroded armature material, eroding rails at the arc strike location and oxidizing, via heating, areas surrounding the arc strike. As damage accumulates, the gun becomes less reliable on subsequent shots and bore life is diminished. The present invention will dramatically increase bore life by allowing projectiles to be fired hundreds of shots with minimal arcing and wear damage to both rails and armatures.
Lubrication is a primary approach for reducing damage to sliding contacts for electromechanical devices, however, there have been few efforts to date to determine the efficacy of lubricants in the specific application of rail guns. Traditional hydrocarbon lubricants are ineffective, both because they are non-conducting and ignitable. Solid lubricants based on graphite have been discussed in the literature, but none has been demonstrated to work effectively. One problem with graphite and metal-graphite solids is that their transfer films are patchy, and since graphite can be very resistive, patches can result in large voltage drops along the interface. Other solids like molybdenum disulphide and other dichalcogenides are lubricous, but not very conductive. Finally, the polymer polytetrafluoroethylene (“PTFE”—best known by the commercial name Teflon®) is a low friction material, but it is a poor conductor (as a bulk solid, it is 1018 times less conductive than Cu). Thin conductive metal films can act as lubricants in solid vs. solid sliding contacts so long as the metal film has much lower shear strength than either metal. The problem remains of how to ‘coat’ the solids with the film run after run, which then presents another problem that hasn't been addressed of how to provide lubrication of the gun during or after each firing.